High-risk Hematologic Malignancies Research Articles

Detailed Assessment of Blood Culture and Clinical Factors in Febrile Neutropenia Patients with High-Risk Hematological Malignancy in Japan: A Subgroup Analysis of the Cedmic Trial

Background: During chemotherapy for hematological malignancies, febrile neutropenia (FN) is a frequent and serious complication. The causative organisms of FN vary from era to era and depending on bacterial resistance in each country. Therefore, epidemiological data are required for each era and country from prospective large clinical trials. We previously reported a prospective clinical trial indicating the importance of the D-index, a measure of neutropenia severity (CEDMIC trial, J Clin Oncol. 2020 10; 38: 815). We hypothesized that analyzing these data would provide accurate contemporary epidemiological data for hematological malignancies. Furthermore, as encountered in practice, we suspected that gram-negative (GN) bloodstream infections (BSIs) are more common at high body temperatures (BTs) than at low BTs and examined the relationship between causative bacteria and BT. Patients and Methods: Between June 2013 and April 2017, we enrolled patients with hematological malignancies aged 16-79 years post-chemotherapy or -stem cell transplantation (SCT) with expected neutropenia durations >7 days. Neutrophil counts <500/mL reflected neutropenia, and all fevers had axillary temperatures ≥37.5°C. Prophylactic antibiotics (Abx) were drugs administered post-chemotherapy and pre-FN onset. The FN incidence and blood culture (BC) positivity rate were examined in 4 treatment groups: allogeneic SCT (Allo-SCT), autologous SCT (Auto-SCT), induction chemotherapy for acute leukemia, and other treatments. Results: In total, 423 patients were enrolled, and 413 (median age: 56 years) were included in the intention-to-treat analyses (Table 1). The treatments included induction chemotherapy (n=67), Allo-SCT (n=106), Auto-SCT (n=158), and others (n=82). Prophylactic Abx were administered in 281 (68.5%) patients (only quinolone, n=222; with β-lactam, n=59). Prophylaxis rates were significantly higher in the Allo-SCT (n=94, 88.7%, p<0.001) and induction chemotherapy (n=49, 73.1%, p<0.017) groups. FN occurred in 356/413 patients (86.4%, Table 1). The Allo-SCT group had a higher FN incidence than that in the other treatments group (93.4% vs. 72%, p<0.001). D-indices ≥5500 and <5500 were associated with FN incidences of 100% and 81.8%, respectively (p<0.001). Prophylaxis did not reduce the FN incidence. In total, 1272 BC sets were collected from 356 patients with FN. At FN onset, BCs were collected from 346 patients; 72 (20.8%) were positive (Table 2). Among initial BCs, 46 (63.9%) harbored gram-positive (GP) and 28 (38.9%) harbored GN bacteria. Three patients had multiple bacterial infections. The 2 most frequent GP bacteria were coagulase-negative Staphylococcus (n=21, 44.7%) and viridans streptococci (n=14, 29.8%). The 3 most frequent GN bacteria were Escherichia coli (n=13, 44.9%), Klebsiella pneumoniae (n=4, 13.8%), and Pseudomonas aeruginosa (n=4, 13.8%). Among initial BCs, prophylactic Abx use did not reduce BC positivity. However, the GN BSI incidence was significantly lower in the prevention group vs. non-prevention group (23.8% vs. 56.7%, p=0.007). Among patients who received prophylactic β-lactam, GN BSIs did not occur. Maximum BTs (maxBTs) were significantly higher in patients with positive BCs than negative BCs (38.4°C vs. 38.0°C, p<0.001). The BTs associated with GN BSIs were significantly higher than those associated with negative BCs and GP BSIs (38.7°C vs. 38.0°C vs. 38.2°C, p<0.001, Figure 1). The maxBTs and BC positivity rates were strongly related (Table 3). The BC positivity rates were significantly higher in patients with BTs ≥38°C vs. <38°C (26.5% vs. 14.5%, p=0.008), 38.5°C vs. >38.5°C/<38.5°C (39.7% vs. 15.3%, p<0.001), and ≥39°C vs. <39°C (52.6% vs. 16.9%, p<0.001). Among patients who did not receive prophylactic Abx (n=106), the GN BSI positivity rate was significantly lower in patients with maxBTs <38°C vs. ≥38°C (14.3% vs. 76.2%, p=0.007). Conclusion: In FN patients with high-risk hematological malignancies in Japan, the frequency of GP BSIs is high. Prophylactic Abx use reduces the GN BSI risk but not the FN or BSI risk. Fever severity and BC positivity at FN onset are strongly associated. The BTs of patients with GN BSIs are high. Disclosures Kanda: Astellas Pharma: Honoraria, Research Funding; Sanofi: Honoraria, Research Funding; Meiji Seika Kaisha: Honoraria; Merck Sharp & Dohme: Honoraria; Pfizer: Honoraria, Research Funding; Shionogi: Research Funding; Celgene: Honoraria; Sumitomo Dainippon Pharma: Honoraria; Eisai: Honoraria, Research Funding; Novartis: Honoraria; Kyowa Kirin: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria; Takeda Pharmaceuticals: Honoraria; Alexion Pharmaceuticals: Honoraria; Shire: Honoraria; Daiichi Sankyo: Honoraria; Ono Pharmaceutical: Honoraria; Nippon Shinyaku: Honoraria, Research Funding; Mochida Pharmaceutical: Honoraria; Otsuka: Honoraria, Research Funding; Chugai Pharma: Honoraria, Research Funding; Janssen: Honoraria; Mundipharma: Honoraria. Kimura:Takeda Pharmaceuticals: Honoraria; Astellas Pharma: Honoraria; Pfizer: Honoraria; Sumitomo Dainippon Pharma: Honoraria; Merck Sharp & Dohme: Honoraria; Nippon Kayaku: Honoraria; Kyowa Hakko Kirin: Honoraria; Ono Pharmaceutical: Honoraria; Celgene: Honoraria; Asahi Kasei: Honoraria. Oyake:Astellas Pharma: Honoraria; Bayer: Research Funding; Chugai Pharma: Honoraria, Research Funding; Celgene: Honoraria; Kyowa Hakko Kirin: Honoraria, Research Funding; Sumitomo Dainippon Pharma: Honoraria; Bristol-Myers Squibb Japan: Honoraria; Pfizer: Honoraria; Sionogi: Research Funding. Tamura:Asahi Kasei: Honoraria; Ono Pharmaceutical: Honoraria; Eisai: Honoraria; Kyowa Hakko Kirin: Honoraria.

A Phase 1 Single Dose Escalation Study of Palifermin Administered Pre-Transplant Conditioning in Subjects Undergoing Matched Unrelated Donor Allogeneic Hematopoietic Stem Cell Transplantation

Background: Early initiation of graft-versus-host disease (GvHD) is driven by donor alloreactive T-lymphocytes directed against recipient's histocompatibility antigens often overexposed during damage to tissues during the conditioning chemotherapy. Palifermin is a truncated form of human recombinant keratinocyte growth factor (KGF, also known as FGF7) that binds to FGF receptor 2b expressed in many epithelia including the epithelium of the epidermis, oral and GI mucosa, urothelium, and thymus, in which it exerts cytoprotective and regenerative effects. Palifermin also has immunomodulatory effects manifested as improvements in thymic function and downregulation of pro-inflammatory cytokines. Palifermin was FDA approved in 2004 at a dose of 60 mcg/kg/day (x3 consecutive days) for prevention of severe oral mucositis in hematologic malignancy patients receiving autologous hematopoietic stem cell transplant (HSCT). A single dose of 180 mcg/kg/day appears to have similar effects. In animal models, palifermin showed efficacy in controlling acute and chronic GvHD. However, subsequent clinical studies did not confirm efficacy for prevention of GvHD or for stimulation of functional thymus recovery using a dose/schedule based on the one that had been approved for autologous HSCT. We conducted a phase 1 study (NCT02356159) to determine the maximal safe single dose level of palifermin administered prior to starting transplant conditioning. Methods: This was an open-label, dose escalation study with standard 3+3 design. Four different dose levels of palifermin (180, 360, 540 and 720 µg/kg) were administered as a single dose on day -7 pretransplant. The reduced-intensity conditioning regimen (cyclophosphamide 1200 mg/m2/day IV and fludarabine 30 mg/m2/day IV), was given on days -6 to -3. Sirolimus, tacrolimus and low-dose post-HSCT methotrexate were used for GvHD prophylaxis. On day 0 all subjects received a peripheral blood stem cell (PBSC) graft from an unrelated donor (MUD) matched at least at HLA-A, -B, -C, -DRB1. Prior to transplant, subjects received one or two cycles of disease-specific lymphodepleting induction chemotherapy (EPOCH-F/R or FLAG). Subjects must have been ≥18 years old with a high-risk hematologic malignancy, Karnofsky performance status ≥60%, and acceptable organ function. The primary objective was to assess safety of palifermin and to recommend the phase 2 study dose. DLT was defined as non-relapse mortality before day 30 post-HSCT regardless of attribution to palifermin and non-hematologic grade ≥4 adverse events (AEs) occurring within 14 days after administration. AEs were recorded according to CTCAEv4. Results: From Oct 2015 to Mar 2019, 18 subjects were enrolled (NHL=7, AML/MDS=5, ALL/LBL=2, CML=2, MPN=1 and MM=1). Kahl's relapse risk was high, standard, and low in 15, 2, and 1 subject, respectively. Median HCT-CI score was 1 (0-4) with median age 47 years (21-66); 14 (78%) were males. Six subjects received dose level 1 (subject #3 was diagnosed with achalasia and grade 4 elevated lipase without radiological signs of pancreatitis, still attributed as DLT possibly related to palifermin). No DLTs occurred afterwards. Three subjects were enrolled onto each of dose levels 2, 3 and 4, with expansion of dose level 4 to 3 more subjects for additional safety exploration. Skin rash and Increased serum amylase or lipase were the most frequent AEs (Table 1A). Grade 3 increased serum amylase and grade 3 possible pancreatitis in subject #3 were the only SAEs attributed to study drug. All subjects engrafted successfully. Day 14 median CD3 and myeloid chimerism was 97% (36-100) and 99% (82-100), respectively, with the median time to 100% CD3 chimerism of 44 days (14-181). Table 1B lists occurrence of GvHD prior to any malignancy relapse. Four subjects had relapsed malignancy, for which 3 received DLI. After a median follow up of 28 months (2-55), 5 subjects have died, 2 malignancy relapses and 3 non-relapse related causes. Conclusion: Palifermin administered at dose four-times higher than previously given in humans is safe to use in patients undergoing MUD peripheral blood HSCT. MTD was not reached. Recommended phase 2 dose for examining efficacy in prevention of GvHD is 720 µg/kg. Disclosures Rubin: NIH/NCI: Ended employment in the past 24 months, Patents & Royalties; KGF/palifermin: Patents & Royalties; Paradigm Shift Therapeutics: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: Palifermin was FDA approved at a dose of 60 mcg/kg/day (x3 consecutive days) for prevention of severe oral mucositis in hematologic malignancy patients receiving autologous hematopoietic stem cell transplant (HSCT).

Salicylates Potentiate and Broaden CRM1 Inhibitor Anti-Tumor Activity Via S-Phase Arrest and Impaired DNA-Damage Repair

Chromosome region maintenance protein1 (CRM1) mediates protein export from the nucleus and is a new target for anti-cancer therapeutics. Broader application of KPT-330 (selinexor), a first in class CRM1 inhibitor recently approved for multiple myeloma and diffuse large B-cell lymphoma (DLBCL), has been limited by substantial adverse effects (AEs). To address this clinical problem, we focused on identifying novel strategies to boost the potency, reduce toxicity, and broaden the applicability of CRM1 inhibitors to a wider range of malignancies. We discovered that salicylates could markedly enhance the anti-tumor activity of CRM1 inhibitors by extending the mechanisms of action beyond CRM1 inhibition. KPT-330 was chosen as the prototypical CRM1 inhibitor given its current FDA approval status and characterized pharmacokinetics; and choline salicylate (CS) was chosen as the prototypical salicylate given its favorable pharmacokinetics and reduced antiplatelet, renal, neurological and gastrointestinal AEs in humans compared to other salicylates. By using cell lines belonging to different hematologic malignancies and solid tumors, we demonstrated ex vivo that the combination of KPT-330 and CS (K+CS) could induce unique and significant antitumor effect at much lower dose of KPT-330 (at 25% of the dose used in the clinic), thereby potentially mitigating prohibitive clinical AEs (Figure 1a-d, and e-g). This significant synergetic antitumor effect observed with K+CS ex vivo was also validated in vivo by using an NSG mouse model of mantle cell lymphoma (Figure 1h). Moreover, the K+CS combination did not show this potent toxic effect on non-malignant cells in vivo and was safe without inducing toxicity to normal organs in NSG mice. Mechanistically, protein profiling through mass spectroscopy revealed that K+CS uniquely affects the cellular pathways of DNA damage repair, DNA synthesis and cell cycle progression. Studies involving immunoblotting, cell cycle analysis, immunofluorescence microscopy assessing nucleocytoplasmic molecular export and DNA damage, reporter assay to assess homologous recombination repair proficiency and immunohistochemistry showed that, compared to KPT-330 treatment alone, K+CS decreased the expression of CRM1, Rad51 and thymidylate synthase proteins in vitro and in vivo, leading to more efficient inhibition of CRM1-mediated nuclear export, impairment of DNA-damage repair, reduced pyrimidine synthesis, and importantly a unique cell cycle arrest in S-phase, thus leading to cell apoptosis. These effects on cellular proteins and pathways were unique to K+CS treatment and were not observed with KPT-330 or CS single agent treatment. Pathway analyses through RNA sequencing also paralleled the findings of proteomic studies thus further validating the unique effect of K+CS treatment on the aforementioned cellular pathways. Importantly, K+CS treatment exerted unique and significant antitumor effect ex vivo on primary malignant cells obtained from patient's with high-risk hematologic malignancies such as double hit DLBCL, BTK and BCL2 inhibitor resistant mantle cell lymphoma, TP53 deleted/mutated chronic lymphocytic leukemia and high-risk multiple myeloma thus signifying its broader applicability as a treatment option for these aggressive hematologic malignancies where there is a dire need to find new treatment strategies (Figure 1i). In summary, we describe a unique all-oral drug combination with a novel constellation of mechanisms of action on cellular pathways that are exploited by cancer cells. K+CS represents a new class of therapy for multiple cancer types and will stimulate future investigations to exploit DNA-damage repair and nucleocytoplasmic transport for therapy of blood cancers. Disclosures Witzig: Karyopharm Therapeutics: Research Funding; Acerta: Research Funding; Incyte: Consultancy; AbbVie: Consultancy; Celgene: Consultancy, Research Funding; MorphSys: Consultancy; Immune Design: Research Funding; Spectrum: Consultancy.

Incidence of Invasive Fungal Infection (IFI) in ACUTE Myeloid Leukemia (AML) on Primary Prophylaxis with Voriconazole in Tertiriary Care Center in Pakistan

OBJECTIVE: The aim of this study was to establish the incidence of IFI in AML patients receiving voriconazole prophylaxis in developing country. METHOD: This prospective study was conducted at The Children's Hospital, Lahore from July 2019 to December 2019 under Prospective AML registry approved by Institutional Review Board. All, consecutive patients of AML, either newly diagnosed or previously diagnosed cases with persistent fever and prolonged neutropenia, were included. Moreover, all patients of AML receiving chemotherapy also received voriconazole prophylaxis. Data of 64 patients was computed in accordance with age, gender, FAB classification, chemotherapy regimen and anti-fungal therapy. EORTC/MSG criteria was used to determine and classify IFI as proven, probable, or possible after performing CT chest and PNS, x-ray PNS, and abdominal ultrasound. CT scan was independently reviewed by a trained radiologist. Data was analyzed by SPSS version 22. RESULTS: Total 64 patients of AML were included in the study. The mean age of presentation was 6 years, range 1.5years to 16 years with 45 % males. Out of 64 patients, fungal infection was suspected in 50 patients (78%) due to persistent fever and prolonged neutropenia. In suspected 50 patients, probable and possible fungal infections were found in 22(34.37%) Patients. Eighteen 18/22 (81.81 %) were probable and 4/22 (18.18 %) were possible fungal infection. Majority of the cases 13/22 (59%) patients developed fungal infection during or after course of first induction therapy. CONCLUSION: Patients with high-risk hematologic malignancies especially AML are more at risk to develop IFI. In our study despite primary prophylaxis with voriconazole, incidence was higher than that reported in the literature from developed countries. Our data suggests that there is need to further improve supportive care measures and implement IFI preventive measures to decrease the incidence of IFI and improve survival. Disclosures No relevant conflicts of interest to declare.

Orca-T, a Precision Treg-Engineered Donor Product, Prevents Acute Gvhd with Less Immunosuppression in an Early Multicenter Experience with Myeloablative HLA-Matched Transplants

Orca-T, a Precision Treg-Engineered Donor Product, Prevents Acute Gvhd with Less Immunosuppression in an Early Multicenter Experience with Myeloablative HLA-Matched Transplants

Pre-Transplant Gene Expression May Predict Risk of Graft Versus Host Disease

Background Allogeneic Hematopoietic Cell Transplantation (allo HCT) is currently the only curative therapy for high-risk hematologic malignancies due to graft versus tumor effect (GVT), but with the cost of Graft Versus Host Disease (GVHD). Despite extensive research, very few predictors of GVHD have been identified to date. To study the mechanisms of GVHD and GVT and to identify potential GVHD markers we applied a novel approach, called Transcriptome Fingerprint Assay (TFA), relying on high frequency sampling and blood transcriptome profiling. The TFA is a multiplex microfluidics q-PCR based assay, linked to a computational model for functional analyses, uniquely tailored to answer complex questions on immune perturbations through frequent profiling of gene expression signatures (Chaussabel et a 2014, Speake et a 2017). This approach has been successfully applied to stratify patients' prognosis in autoimmune and infectious diseases. Herein we report the discovery of an association between the expression abundance of a set of genes pre-transplant and the development of acute or chronic GVHD. Methods Seventy-eight patients candidate to allo-HCT were enrolled on the study. Patients donated micro-quantities of blood (50-600 microliters) prior to transplant conditioning, weekly until day 100 post-transplant and every 2 weeks thereafter until 2 years after transplant. Detailed clinical, laboratory and therapy annotations are captured during the follow-up. Gene expression of 264 immune-related genes for each sample are measured through Fluidigm BioMark high-throughput qPCR system. Data interpretation is performed through TFA modular analyses and correlated with the clinical annotations. Here we report the univariate analysis of gene expression data and its association with GVHD in 31 patients for whom data are available until at least day 169 post-transplant (169-672, median 513). SIgnificant genes were tested in a longitudinal analysis with 4 combined linear-mixed models, measuring the parameters: 1) groups (GVHD NO-GVHD) 2) time 3) interaction of groups over time. Results Patients' characteristics are summarized in Fig 1; 26 patients developed GVHD (12 acute GVHD only, 3 late acute GVHD, 1 overlap syndrome, 5 acute and chronic GVHD and 5 chronic GVHD only). By TFA analysis of pre-transplant samples, we identified 3 genes significantly downregulated among patients who developed GVHD (GPSM3, LRG1 and EPHX4), and 2 genes borderline (<1.5 folds) upregulated (IFI35, PLK3). Among these, GPSM3 (an MHC regulated gene) has shown to have alleles protective against severe autoimmune diseases as RA, and LRG1 to facilitate CD34 and myeloid progenitors growth by antagonizing TGF-beta effects, but also to be upregulated in GVHD patients. Several other genes (111) were found to be >1.5 fold upregulated in the GVHD group, but with a non-significant p-value (Volcano-plot Fig.1). Of note, 12 of them were >4 fold upregulated, and their transcriptome pertains to B cells, T lymphocytes, monocytes, IFN, TNF, other cytokines and neutrophil activation. Moreover, among these genes IFN-genes were consistently represented by multiple IFN-modules, emerging as promising candidates. Longitudinal analyses confirmed that EPHX4 and GPSM3 distinguished the cohorts for all the measured parameters in the post-transplant time. EPHX4 increased over time in both groups but significantly more in the NO-GVHD group (with a fixed effect estimate of 2.05); GPSM3 instead decreased over time, again significantly more in the NO-GVHD group (with a fixed effect estimate of -0.95). LRG3 showed significance only for the parameter "time", resulting after transplant more abundant in the GVHD group, thus confirming previous literature data. IFN modules were also tested longitudinally, showing very distinct patterns in the cohorts, and several significant genes (IFI27, NT5C3, CCR1, LBA1, Fig.1) Conclusion Our data demonstrate that TFA may be used to assess expression of immune related genes in transplant patients and to identify specific pathways that may be predictive for GVHD development. Additional work is required to validate our data in a larger cohort and for better understanding of the role of those genes in triggering or protecting against GVHD. Upon completion of the study and the longitudinal analyses, we aim to define in depth transcriptome signatures of GVHD and relapse. Disclosures No relevant conflicts of interest to declare.

Myeloablative haploidentical BMT with posttransplant cyclophosphamide for hematologic malignancies in children and adults

AbstractPromising results have been reported for patients with high-risk hematologic malignancies undergoing HLA-haploidentical bone marrow transplantation (haploBMT) with posttransplantation cyclophosphamide (PTCy), but there are few data on outcomes with myeloablative conditioning in this context. We report the results of a single-institution, prospective phase 2 trial of myeloablative haploBMT using busulfan-based or total body irradiation–based conditioning in 96 children or adults (median age, 42 years; range, 1-65 years) with high-risk hematologic malignancies. Recovery of neutrophils and platelets occurred at a median of 24 and 29 days. Engraftment of donor cells with chimerism >95% was achieved in 91%. The cumulative incidence of acute graft-versus-host disease (GVHD) grades II to IV and grades III to IV at day 100 was 11% and 4%, and of chronic GVHD at 6 and 12 months was 4% and 15%, with 6% moderate to severe. The cumulative incidence of nonrelapse mortality was 6% at 100 days and 11% at 1 year (19% in those aged >55 years). The cumulative incidence of relapse at 1 year was 35%; at 3 years, it was 43%. In multivariable analysis, relapse was associated with increased age (P= .02 for age 20-55 years andP= .02 for age >55 years) and with minimal residual disease before transplantation (P= .05). The overall survival at 1 and 3 years is 73% and 54%, and event-free survival at 1 and 3 years is 57% and 49%. We show that haploBMT with PTCy after myeloablative conditioning is safe and efficacious for adult and pediatric patients with hematologic malignancies. Careful consideration must be given to using myeloablative conditioning in patients age >55 years. This trial was registered atwww.clinicaltrials.govas #NCT00796562.

T-Cell Replete Myeloablative Haploidentical Bone Marrow Transplantation Is an Effective Option for Pediatric and Young Adult Patients With High-Risk Hematologic Malignancies.

Twenty-one pediatric and young adult patients (1.1–24.7 years) with hematologic malignancies underwent myeloablative T-cell replete haploidentical bone marrow transplant (haplo-BMT) between October 2015 to December 2019. Fifty-seven percent of the patients were ethnic or racial minorities. Thirteen patients had B-cell precursor acute lymphoblastic leukemia (B-ALL) with 10 receiving 1,200 cGy fractionated total body irradiation with fludarabine while the remaining 11 patients had targeted dose-busulfan, fludarabine, melphalan conditioning. Graft-vs.-host disease (GvHD) prophylaxis consisted of post-transplant cyclophosphamide (15 patients) or cyclophosphamide and bendamustine (six patients), with all patients receiving tacrolimus and mycophenolate mofetil. Twelve patients were in first or second remission at time of transplant with five in >2nd remission and four with measurable disease. Three patients had failed prior transplants and three CAR-T cell therapies. Only one patient developed primary graft failure but engrafted promptly after a second conditioned T-replete peripheral blood stem cell transplant from the same donor. An absolute neutrophil count of 0.5 × 109/L was achieved at a median time of 16 days post-BMT while platelet engraftment occurred at a median of 30 days. The cumulative incidence of grades III to IV acute GvHD and chronic GvHD was 15.2 and 18.1%, respectively. With a median follow-up of 25.1 months the relapse rate is 17.6% with an overall survival of 84.0% and a progression-free survival of 74.3%. The chronic graft-vs.-host-free relapse-free survival (CRFS) is 58.5% while acute and chronic graft-vs.-host-free relapse-free survival (GRFS) is 50.1%. Myeloablative conditioned T-replete haploidentical BMT is a viable alternative to matched unrelated transplantation for children and young adults with high-risk hematologic malignancies.

The Role of Immune Checkpoints after Cellular Therapy.

Cellular therapies utilize the powerful force of the human immune system to target malignant cells. Allogeneic hematopoietic stem cell transplantation (allo-HCT) is the most established cellular therapy, but chimeric antigen receptor (CAR) T cell therapies have gained attention in recent years. While in allo-HCT an entirely novel allogeneic immune system facilitates a so-called Graft-versus-tumor, respectively, Graft-versus-leukemia (GvT/GvL) effect against high-risk hematologic malignancies, in CAR T cell therapies genetically modified autologous T cells specifically attack target molecules on malignant cells. These therapies have achieved high success rates, offering potential cures in otherwise detrimental diseases. However, relapse after cellular therapy remains a serious clinical obstacle. Checkpoint Inhibition (CI), which was recently designated as breakthrough in cancer treatment and consequently awarded with the Nobel prize in 2018, is a different way to increase anti-tumor immunity. Here, inhibitory immune checkpoints are blocked on immune cells in order to restore the immunological force against malignant diseases. Disease relapse after CAR T cell therapy or allo-HCT has been linked to up-regulation of immune checkpoints that render cancer cells resistant to the cell-mediated anti-cancer immune effects. Thus, enhancing immune cell function after cellular therapies using CI is an important treatment option that might re-activate the anti-cancer effect upon cell therapy. In this review, we will summarize current data on this topic with the focus on immune checkpoints after cellular therapy for malignant diseases and balance efficacy versus potential side effects.

Patient-reported outcomes in acute graft-versus-host disease: optimizing patient care and clinical trial endpoints.

Patient-reported outcomes (PROs) refer to patient perceived and reported health-related quality of life (HRQOL), functional status, and symptom burden. PROs have become an important measure in oncologic care to identify the impact of the disease and its treatment on a patient's health status. Hematopoietic cell transplantation (HCT) is an aggressive and potentially curative therapy for patients with high-risk hematologic malignancies. A common complication of HCT is graft-versus-host disease (GVHD), which can be a significant contributor to morbidity and mortality, as well as a wide spectrum of physical and psychosocial effects. Quality of life and symptom burden have been shown to be important measures in the study of posttransplant complications, including chronic GVHD. We review the need for a novel tool in acute GVHD to capture disease symptoms and HRQOL to better understand patient symptoms, disease trajectory and outcome.

Donor Heme Oxygenase-1 Promoter Gene Polymorphism Predicts Survival after Unrelated Bone Marrow Transplantation for High-Risk Patients.

Heme oxygenase-1 (HO-1), an intracellular enzyme that catalyzes the degradation of heme into biliverdin, free iron, and carbon monoxide, exerts anti-inflammatory and cytoprotective effects against endothelial cell injury. The HO-1 promoter gene has one important single-nucleotide polymorphism (SNP) rs2071746 (-413A>T) that is functional, and the A allele has been reported to be associated with higher HO-1 expression levels than the T allele. We investigated the influence of the HO-1 rs2071746 SNP on the transplant outcomes in 593 patients with hematological malignancies undergoing unrelated, human leukocyte antigen (HLA)-matched, T-cell-replete bone marrow transplantation (BMT) through the Japan Donor Marrow Program. In patients with high-risk diseases, the donor A/A or A/T genotype was associated with better 5 year overall survival (35% vs. 25%; p = 0.03) and 5 year disease-free survival (35% vs. 22%; p = 0.0072), compared to the donor T/T genotype. These effects were not observed in patients with low-risk diseases. The current findings therefore indicate that HO-1 rs2071746 genotyping could be useful for selecting donors and tailoring transplant strategies for patients with high-risk hematologic malignancies.

Mgta-456, a Cell Therapy Utilizing Expansion of CD34+ Hematopoietic Stem Cells (HSC), Improves HLA Matching for Adult Recipients, Promotes Faster Hematopoietic Recovery and Enables Uniform Engraftment with Less Acute Graft-Vs-Host Disease (GVHD)

<h3>Background</h3> HSC dose and HLA match are risk factors that impact mortality using cord blood units (CBU) in transplant. Low CD34+ doses result in prolonged cytopenia and higher graft failure risk. A minimum cell dose of 3.0 × 10⁷ total nucleated cells (TNC)/kg has generally been required in CBU selection; however, cell dose limits often require the use of a 2^nd unit and markedly limits the availability of 7-8/8 HLA-matched units in larger patients. MGTA-456 is a cell therapy product utilizing an aryl hydrocarbon receptor antagonist for expansion of CD34+ HSCs <i>in vitro</i>. In prior studies with fresh MGTA-456, 36 patients with hematologic malignancies demonstrated rapid neutrophil recovery and 100% engraftment. This study (NCT03674411) will evaluate the safety and efficacy of cryopreserved MGTA-456 and the effectiveness of lowering the TNC threshold of the selected CBU to 1.0 × 10⁷ TNC/kg before expansion to improve HLA match. <h3>Methods</h3> 13 patients aged 2-47 years (12-159 kg) with high-risk hematologic malignancy were enrolled with 11 transplanted to date. Patients received cyclophosphamide 120 mg/kg, fludarabine 75 mg/m2 and total body irradiation 1320 cGy or a busulfan-based regimen for children ≤3 years of age prior to MGTA-456 with cyclosporine/mycophenolate mofetil prophylaxis. G-CSF began the day after infusion until the neutrophil count exceeded 2500/uL for 3 days. <h3>Results</h3> MGTA-456 contained a median 2.3 × 10⁹ CD34+ cells (range, 0.65-8.0) after expansion (422-fold expansion of CD34+ cells [range, 219-1313]). Neutrophil recovery occurred in all patients with a median of 15 days (range, 0-31), similar to recipients of fresh MGTA-456 in a prior study (median 14 days) and significantly faster than in recipients of unmodified CBUs (median 25 days). Median platelet recovery was 41 days (range 24-49) vs 64 days with unmodified CBUs. MGTA-456 CD34+CD90+ content strongly correlated with speed of neutrophil recovery (Fig. 1), consistent with preclinical murine data showing CD34+CD90+ cells represent the true engraftable HSC population. Lowering the TNC requirement to 1.0 × 10⁷ TNC/kg for CBU selection pre-expansion improved HLA match and/or eliminated the need for double CBU transplant in all 5 patients weighing >80 kg. Three patients received 8/8 grafts who would have otherwise received 1 or 2 6/8 units (n=2) or two 7/8 units (n=1) which may account for the low incidence of aGVHD overall (3 cases of Grade 1-2 and no Grade 3-4). With a follow-up of 5.2 months (0.4-8.5 months), all patients are alive. <h3>Conclusion</h3> Cryopreserved MGTA-456 cell therapy resulted in rapid and 100% engraftment with speed of neutrophil recovery correlating with CD34+CD90+ cell dose in patients with high risk hematologic malignancy. Expansion of smaller CBUs increases the chance of finding a better HLA match, particularly for adults, thus reducing the barriers associated with low cell dose and poor HLA match in CBU transplantation.

Predictors of Relapse after Haploidentical Hematopoietic Progenitor Cell Transplantation (Haplo-HCT); A Single-Institution Experience

<h3>Background</h3> Haplo-HCT emerged as a reliable option for patients with high risk hematological malignancies with no HLA-matched related or unrelated donors available. Retrospective registry data suggest comparable outcomes to HLA-matched donors; however, relatively little is known regarding predictors of disease relapse following haplo-HCT. We hypothesize that attainment of full-donor CD3 and CD33 chimerism at day 30 (D30) and 100 (D100) is associated with lower incidence of relapse after haplo-HCT. <h3>Methods</h3> We undertook a retrospective analysis of 78 patients who underwent haplo-HCT at the Ohio State University James Cancer Hospital between January 2013 and December 2017. The associations between patient characteristics including CD3/CD33 donor chimerisms and the cumulative incidence rate (CIR) of relapse were evaluated using proportional sub-distribution hazards model, treating death without relapse as the competing risk. The models were built adopting a landmark analysis approach at D30 and D100. Progression-free survival (PFS) was estimated using the method of Kaplan-Meier. <h3>Results</h3> Median age at haplo-HCT was 56 (20-74) years and 68% were males. 50% had acute myeloid leukemia/myelodysplastic syndrome, and 54% had intermediate disease risk index (DRI). Most patients (85%) received reduced-intensity conditioning and 50% received bone marrow (BM) grafts. Complete (100%) CD3 donor chimerism was observed in 63 (84%) patients at D30, and subsequently 59 (95%) patients at D100. Complete CD33 donor chimerism was observed in 67 (89%) patients at D30, and subsequently 56 (88%) patients at D100. In univariable D30 landmark analysis, the CIR of relapse was significantly lower in patients who achieved complete CD3 (and CD33) chimerism compared with patients with less than complete chimerism (Figure 1A; p<0.01 and p<0.01, respectively). Attainment of complete CD3 chimerism at D30 was also associated with PFS (Figure 1B; p<0.01). However, in multivariable analysis, complete CD3 chimerism at D30 was no longer independently associated with the CIR of relapse due to its high correlation with DRI (p=0.01). Receipt of a BM graft was associated with significantly higher CIR of relapse both in univariable and multivariable analyses (HR 2.43, 3.34; p=0.05, 0.01, respectively). D100 complete CD33 chimerism conferred a significant CIR advantage in both univariable (p<0.01) and multivariable (p<0.01) models, although CD3 chimerism did not retain significance (p=0.35). <h3>Conclusions</h3> Complete CD3 and CD33 donor chimerisms at D30 and D100 predict a patient's risk for relapse following haplo-HCT. We observed a strong association between CD3 chimeric status at D30 with DRI, as well suggestive that high risk disease may be associated with impaired immune reconstitution after transplant and perhaps a less robust graft vs disease effect.

UM171 Expansion Overcomes Shortcomings of Cord Blood Transplantation While Maintaining Benefits

Background Benefits of cord blood (CB) transplantation include low rates of relapse and chronic graft-versus-host disease (GVHD). However, CB use has rapidly declined because of the high rates of infections, severe acute GVHD, and transplant-related mortality (TRM) as well as prolonged hospitalization. We therefore initiated a clinical trial with UM171, a potent agonist of hematopoietic stem cell (HSC) self-renewal, to attempt to solve these limitations and permit transplantation of smaller, better HLA-matched CBs. Methods Expansion culture lasted 7 days and patients received a myeloablative conditioning regimen followed by a single CB transplant including both the expanded CD34+ cells and the lymphocyte-containing CD34- fraction. Results Between 9/16-11/18, 22 adults with mostly high- to very high-risk hematologic malignancies were transplanted. Median transplant co-morbidity index was 2 (0-5). Five patients had already failed an allogeneic transplant, 3 patients had acute leukemia not in remission, and 2 patients had relapsed/refractory aggressive lymphoma. UM171 treatment profoundly changed the cellular composition of the graft, including a 600 and 8000-fold increase in dendritic and mast cell progenitors, respectively. Neutrophil engraftment was prompt with median time to 100 and 500 neutrophils/μL of 9.5 and 18 days, respectively. Patients seemed to derive clinical benefit from achieving 100 neutrophils rapidly translating into early resolution of febrile neutropenia (median day 7) contributing to shorter hospitalization when compared to conventional CB transplants at same institution with larger cell doses and similar time to 500 neutrophil engraftment. Median CD4 counts at 3 and 12 months were 218 and 413/μL, respectively. Incidence of grade 3-4 acute GVHD was low (9%) and there was no steroid refractory GVHD or moderate-severe chronic GVHD. More than 90% of patients were off immunosuppressive therapy by 12 months. One patient died of TRM ( Conclusions A 7-day UM171 expansion CB protocol is feasible and provides clinical benefits beyond engraftment, such as very low TRM. If confirmed, UM171 expansion may overcome the shortcomings of CB transplants while maintaining its benefits of low risk of chronic GVHD and relapse. We have now embarked on a phase 2 trial to confirm if a UM171 modified graft, enriched in dendritic cells, will have a potent antileukemia effect in extremely high-risk patients such as refractory leukemias and high risk mutations (e.g.: p53, EVI-1).

A Single Dose of a Novel Anti-Human Short Half-Life Engineered CD45-Targeted Antibody-Drug Conjugate (ADC) Is Cytoreductive on Patient-Derived Tumors and Extends Survival Beyond Standards of Care in Multiple Pre-Clinical Models of Hematologic Malignancy

For patients with refractory or high-risk hematologic malignancies, like acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), and acute lymphoblastic leukemia (ALL), allogeneic hematopoietic stem cell transplant (Allo-HSCT) is a potentially curative approach. Morbidities and mortality associated with current conditioning regimens limit the use of this curative procedure. As a result, many eligible patients do not consider transplant and 2/3 of those transplanted are only able to tolerate a reduced intensity conditioning regimen, which is associated with increased relapse rates (Scott, J Clin Onc 2017). Thus, there is an urgent need for a safer and more effective conditioning agent with improved disease control. Our targeted antibody drug conjugate (ADC) approach is designed to improve the safety of current conditioning protocols by specifically depleting CD45+ cells. We developed a novel anti-human CD45-targeted short half-life ADC conjugated to amanitin (AM). CD45 is the ideal target for allo-HSCT conditioning because it is expressed on all hematopoietic cells (except erythrocytes, plasma cells and platelets), and most hematologic malignancies. Given their targeted specificity, anti-CD45-AM can potentially provide dual benefit to leukemia patients by combining effective conditioning for HSCT with depletion of target-bearing tumor cells. To demonstrate our engineered short half-life anti-human CD45-AM has anti-leukemic activity we tested it in human leukemic xenograft murine models. A panel of models were evaluated to mimic untreated and refractory disease; AML PDX models (from treatment naïve and relapsed post allogeneic HCT patients), ALL cells from an immortalized cell line (REH-Luc), T-ALL patient-derived xenograft (PDX) model (from a patient progressing post DHAP chemotherapy). In the REH-Luc model, single doses of anti-CD45-AM were well tolerated, and cytoreductive resulting in delayed tumor growth compared to vehicle (PBS), isotype-AM, or standard of care (SoC) doxorubicin. Anti-CD45-AM treatment in the PDX AML, and T-ALL significantly decreased peripheral tumor burden resulting in delayed tumor growth compared to vehicle, isotype-AM, and comparable to 2 clinically validated standards of care (Ara-C, and dexamethasone respectively; figure 1). As designed for the transplant indication, the ADC had a reduced half-life compared to wild type antibody controls (16 vs 79h). These data in humanized murine xenograft models demonstrate that short half-life CD45-AM ADCs are potent targeted anti-leukemia agents. Together with prior reports demonstrating the potency of anti-CD45-AM as conditioning agents, these non-genotoxic ADCs may be useful in reducing disease burden and inducing durable remissions in patients after transplant particularly those who receive reduced intensity conditioning that are at high risk of relapse.

Nicotinamide (NAM) Modulates Transcriptional Signature of Ex Vivo Cultured UCB CD34+ Cells (Omidubicel) and Preserves Their Stemness and Engraftment Potential

Historical efforts at expansion of umbilical cord blood (UCB) derived CD34+ hematopoietic stem cells (HSCs) ex vivo with cytokines yielded large numbers of progenitors for transplantation but impaired their long-term engraftment. We used nicotinamide (NAM), an allosteric inhibitor of NAD-enzymes, to create omidubicel, an investigational cell therapy designed to improve the expansion of CD34+ HSCs for bone marrow transplant. A Phase 1/2 clinical study in patients with high-risk hematologic malignancies showed rapid neutrophil engraftment in patients compared to historical controls [1]. We hypothesized that NAM treatment maintains the stemness and engraftment potential of omidubicel, which is associated with clinical benefit [2]. We performed transcriptome analysis to discern the mechanism of action of NAM after ex vivo expansion of CD34+ cells in omidubicel compared to CD34+ controls. Analysis revealed that HSCs expanded with cytokines alone led to an increase in genes responsible for cell proliferation, differentiation, and apoptosis, and in the production of reactive oxygen and nitrogen species (ROS, RNS), and matrix metalloproteinases (MMPs), all of which were attenuated by NAM. Transcription factor (TF) enrichment analysis demonstrated that NAM modulated TFs critically involved in activation of pathways for HSC differentiation, apoptosis, and migration. Specifically, NF-kB, C-Jun, LXR/RXR and PPARα/RXRα, and mTor signaling were all reduced in NAM-treated CD34+ cells compared to controls. NAM treatment upregulated genes linked to cellular metabolism including the Sirtuin family genes, TCA cycle genes, and HIF1a. NAM upregulated genes responsible for telomerase expression further validating our hypothesis that NAM preserves cell stemness. In summary, these data provide further scientific rationale for the favorable clinical engraftment and patient outcomes observed in the Phase 1/2 clinical study of omidubicel. An international, randomized, multi-center Phase 3 study of omidubicel in patients with high-risk hematologic malignancies is underway [2]. [1] Horwitz ME. et. al., J Clin Oncol. 2019 Feb 10;37(5):367-374. [2] ClinicalTrials.gov identifier NCT02730299.

Outcomes of Two Chemotherapy-Based Preparatory Regimens Compared to TBI-Based Conditioning When Used with CD34+ Selected T-Cell Depleted Allohct for High Risk Hematologic Malignancies: Prospective Clinical Trial NCT 01119066

<h3>Introduction</h3> To assess the therapeutic potential of non-TBI conditioning and T-cell depleted (TCD) allo HCT for high risk malignancies, we conducted a prospective trial comparing: A. our standard 1375 cGy HFTBI + Thiotepa, 5mg/kg/dx2 + cyclophosphamide, 60mg/kg/dx2 vs B. Busulfex, 0.8mg/kg/6hx12(PK adjusted) + Melphalan 70mg/kg/dx2 + Fludarabine 25mg/m²/dx5 vs C. Clofarabine 20mg/m²/dx5 + Melphalan 70mg/m²/dx2 + Thiotepa 5mg/kg/dx2 as preparation for T-cell depleted CD34⁺ PBSC allografts isolated by the CliniMACS system. All pts received Thymoglobulin pre-transplant to prevent infection. No GVHD prophylaxis was given post transplant. Pts were stratified to arms A, B or C based on disease stage and clinical factors enhancing TBI risks (e.g. age >60m prior therapy or comorbidities), with Arm B the non-TBI arm used for myeloid malignancies and Arm C for lymphoid malignancies. <h3>Results</h3> From 5/13/10 to 12/31/16, 283 consenting patients were transplanted (106 in Arm A, 144 in B, 33 in C). All pts engrafted by day 10-11; 3 pts in Arm B and 1 in C had late graft failure with sustained T-cell chimerism. The 3 in Arm B reconstituted after TCD PBSC boost alone (N=2) or after CTX/ATG (N=1) conditioning. Cumulative Incidence (C.I.) of Acute Grade 3-4 GVHD was higher in Arm A (12%) than in B (4.2%) or C (3.0%) (p = 0.03), as was C. GVHD (Arm A 8.5%; B (1.5% p = 0.02); C (3%)). CI of relapse at 3 yrs was similar in all arms (A=28%; B=21%; C15%) (p = 0.22). Although pts in Arm B were older (med. 58.5 yrs) than in A (32 yrs) or C(32 yrs), NRM at 3 yrs for Arm B (16%) and A (14.8) were similar. However, NRM in Arm C (32.7%) was higher (p = 0.09). Because the median age of patients in Arm B (58.5 yrs) differed significantly from Arms A (31.9 yrs) and C (32.3 yrs); we evaluated DFS for each arm in 20 year cohorts of increasing age (Fig 1 A,B,C). Because of low cohort size, pts in Arm C aged <40 were compared to those ≥ 40. In Arm A, 5 year DFS rates were 54.2% (Age ≤20), 62.9% (Age>20-40) and 54% (Age 40-60). In Arm B, 5 year DFS for pts ≤ 20 was 69.3% and 85.7% for those >20-40, 48.6% for those >40-60 and 46.8% for those 60+ respectively (p = 0.02). In Arm C, 5 year DFS for pts ≤40 was 65% and for those >40, 30.7% (p = 0.01). <h3>Conclusion</h3> These results demonstrate that these chemotherapy-based regimens secure engraftment and hematopoietic reconstitution and similarly low rates of GVHD and relapse. They also suggest an advantage for patients ≤40 treated on Arm B. In >40-60yo patients, DFS for Arm B is equivalent to Arm A and also yields favorable results in older pts (>60-73 yrs). However, while patients ≤40 yrs of age fared well on Arm C, older patients were less likely to achieve extended OS and DFS than those on Arms A or B, likely as a consequence of increased TRM.

Targeting Danger Associated Molecular Pattern (DAMP) with CD24Fc to Reduce Acute Gvhd: Study Design on a Randomized Double Blind Placebo Controlled Phase III Clinical Trial (CATHY Study)

<h3>Introduction</h3> Allogeneic HCT is the only established curative therapy for high risk hematologic malignancies. The major challenges are leukemia relapse and high grade GVHD. We have developed the CD24Fc fusion protein to selectively inhibit danger-associated molecular pattern (DAMP)-induced inflammation and discovered that it effectively prevents GVHD without affecting the desirable GVL effect in preclinical models. With the support of SBIR awards from the NCI, we have completed a phase II randomized, double blind, multi-center, dose escalation trial comprised of 3 dosing cohorts of 8 patients (3:1 CD24Fc vs. placebo), with a total enrollment of 24 subjects. Notably, clinical data from this trial demonstrate that CD24Fc reduces the incidence of severe GVHD, resulting in statistically significant increases of acute 180-day GVHD-free survival (aGFS). A Phase II expansion cohort to enroll an additional 20 subject is ongoing (NCT02663622). Here we propose a phase III clinical trial with 180 patients (1:1 CD24Fc vs placebo) to test the hypothesis that CD24Fc prophylaxis can significantly improve 180 day acute GVHD-free survival (aGFS) over placebo control. <h3>Study Design</h3> A Randomized, Double-blind, Placebo-controlled, Multi-Center, Phase III Study of CD24Fc for the Prevention of Acute GVHD Following Myeloablative Allogeneic HCT (CATHY) (NCT04095858). This study will compare CD24Fc or Placebo with standard GVHD prophylaxis of tacrolimus and methotrexate in the setting of myeloablative conditioning (MAC), matched unrelated donor (MUD) allogeneic HCT in patients with AML/ALL or MDS. Patients will be randomized 1:1 to receive CD24Fc or placebo at the dose levels of 480mg, 240mg and 240mg on Days -1, +14 and +28, respectively. The primary endpoint is the rate of 180 days grade III-IV acute GVHD-free survival (aGFS). Secondary endpoints are 1 yr DFS, 1 yr OS, and D180 Gr II-IV aGFS. Other exploratory evaluations will be 1 yr chronic GVHD, 1 yr relapse, NRM at 1 year, incidence and rate of infection at 100 days, and rate of Gr III and above mucositis at 28 days. The study will enroll 180 patients, or 90 per arm, with an estimated accrual period of 24 months. <h3>Statistical Consideration</h3> The study will include one interim analysis for efficacy. Z test statistics for comparing the two arms will be compared to the critical values and results be reviewed by the independent DSMB.

Host T-Cells Contribute to Immune Reconstitution and Improved Outcome in Recipients of CD34 Selected T-Cell Depleted Allografts (TCD HCT) with Full Hematopoietic Cell but Persistent Mixed T-Cell Chimerism

<h3>Background</h3> Isolated mixed T-cell chimerism in otherwise fully engrafted recipients of TCDHCT has been associated, in some series, with risk of graft rejection or relapses and an indication for DLI. Thereto, we have analyzed the impact of donor chimerism on outcomes in a prospective clinical trial of conditioning regimens used with CD34+ selected TCDHCT. <h3>Methods</h3> The trial (NCT0119066) compares A) HFTBI, Thiotepa and cyclophosphamide with B) Busulfex, melphalan and fludarabine or C) Clofarabine, melphalan and thiotepa as conditioning for CD34+ TCDHCT used to treat high risk hematologic malignancies. As part of the trial, we sequentially assessed lineage-specific donor chimerism in the marrow and the myeloid cells and T-cells in blood by analysis of donor and host-specific STRs in cell fractions isolated by immunotype. In the landmark analysis, quartiles of donor chimerism were compared for T-cell levels, and clinical outcomes. <h3>Results</h3> 283 consecutive patients, transplanted between 5/13/2010 and 12/31/2016 (106 in Arm A, 144 in Arm B, 33 in Arm C). All engrafted by day 10-11. While 3 pts in Arm B and 1 in C had late graft failure, all others from 3 mos on had full donor chimerism in marrow and myeloid blood cells. However, at 3 mos median donor CD3⁺ T-cell chimerism (MDTC), was mixed in each arm but significantly lower in Arm B (10%) vs A (50%) and C (63%) (p<0.001). While MDTC for Arms A and C rose to 80% and 85% by 6 mos and ≥95% by 1yr, but in Arm B was 25% at 6 mos, 55% at 1 yr and 65% at 2 yrs. To assess the impact of this sustained mixed chimerism, we did a landmark analysis at 3 months, comparing subsequent T-cell recovery and clinical outcomes for pts in the first (lowest) and fourth (highest) quartile of T-cell chimerism in Arms A and B. As shown in Table 1, CD3⁺ and CD8⁺ T-cells in both arms were significantly higher in Q1, as were CD3⁺CD4⁺ cells in Arm B. Non-relapse mortality (NRM) at 2 yrs was also significantly lower for Q1 pts in both arms but relapse risks were not. In Arm B, but not A, 2yr OS and DFS were also significantly better in Q1 vs Q4. <h3>Conclusions</h3> Conditioning with Bu/Mel/Flu (Arm B) secured durable engraftment and hematopoietic reconstitution but a high proportion of pts have isolated and persistent mixed T-cell chimerism. However, surviving host T-cells can expand, persist and contribute significantly to earlier T-cell recovery and long-term reduction of NRM without increasing risk of graft rejection, relapse or need for DLI.

Reduced Toxicity, Myeloablative Conditioning Regimen with Busulfan, Fludarabine, Anti-Thymocyte Globulin and 400 Cgy TBI in Pediatric Patients Undergoing Hematopoietic Stem Cell Transplant for High-Risk Hematologic Malignancies

<h3>Introduction</h3> Myeloablative conditioning (MAC) regimens decrease the risk of relapse in pediatric patients undergoing hematopoietic stem cell transplant (HCT) but cause significant toxicities: transplant-related mortality (TRM) and late effects. Therefore, a MAC regimen that decreases toxicity has the potential to improve overall survival (OS). Busulfan (Bu), fludarabine (Flu), anti-thymocyte globulin (ATG) and 400 cGy of total body irradiation (TBI), a reduced toxicity, MAC regimen was used in pediatric patients. <h3>Objectives</h3> To evaluate the safety and toxicity of this regimen. Secondary objectives included determining OS at 2 and 5 years, and incidence of relapse and GVHD. <h3>Methods</h3> We prospectively evaluated 40 patients ≤21 years of age undergoing HCT for high-risk leukemias who received dose-adjusted Bu, Flu, ATG and TBI. Bu pharmacokinetics were measured after a test dose and regimen dose 1 to target AUC of 4000-5000 uMol*min/day. <h3>Results</h3> Patients were treated between October 2008 and June 2018 (Table 1). OS was 67% and 51% at 2 and 5 years post-HCT, respectively. OS at 2 and 5 years was 70% and 55% for patients with myeloid disease versus 56% and 37% for patients with lymphoid disease, respectively (p=0.18) (Figure 1). Relapse occurred in 11 (28%) at a median of 7 months. TRM was 8% and 13% at 100 days and 1 year post-HCT, respectively. All patients engrafted. >Grade II acute GVHD was seen in 9 (23%); chronic GVHD was seen in 16 (40%). There was no significant impact of age, disease type, donor source or type on HCT outcomes. Long-term toxicities noted were ovarian insufficiency in 8, and short stature, hypothyroidism and learning disabilities in 2 each. Evaluation of Bu AUCs and multivariate analyses are still ongoing. <h3>Conclusions</h3> Reduced toxicity, MAC regimen was well tolerated with a low incidence of TRM. This regimen shows a trend toward better efficacy in patients with myeloid disease, however larger studies are needed.